Anatomically approximate prosthetic mitral heart valve

ABSTRACT

An anatomically approximate prosthetic heart valve includes dissimilar flexible leaflets, dissimilar commissures and/or a non-circular flow orifice. The heart valve may be implanted in the mitral position and have one larger leaflet oriented along the anterior aspect so as to mimic the natural anterior leaflet. Two other smaller leaflets extend around the posterior aspect of the valve. A basic structure providing peripheral support for the leaflets includes two taller commissures on both sides of the larger leaflet, with a third, smaller commissure between the other two leaflets. The larger leaflet may be thicker and/or stronger than the other two leaflets. The base structure defines a flow orifice intended to simulate the shape of the mitral annulus during the systolic phase. For example, the flow orifice may be elliptical. A relatively wide sewing ring has a contoured inflow end and is attached to the base structure in such a way that the valve can be implanted in an intra-atrial position and the taller commissures do not extend too far into the left ventricle, therefore avoiding injury to the ventricle.

CROSS REFERENCE TO A RELATED PATENT APPLICATION

The present application claims priority to U.S. Provisional PatentApplication No. 60/538,516, filed on Jan. 23, 2004, the disclosure ofwhich is incorporated by reference herein in its entirety.

FIELD OF THE INVENTION

The present invention relates generally to medical devices, and moreparticularly to a prosthetic mitral heart valve having an asymmetricperiphery and unequal leaflets.

BACKGROUND OF THE INVENTION

Two primary types of heart valve replacements or prostheses are known.One is a mechanical-type heart valve that uses a ball and cagearrangement or a pivoting mechanical closure supported by a basestructure to provide unidirectional blood flow, such as shown in U.S.Pat. No. 4,306,319 to Kaster. The other is a tissue-type or“bioprosthetic” valve having flexible leaflets supported by a basestructure and projecting into the flow stream that function much likethose of a natural human heart valve and imitate their natural action tocoapt against each other and ensure one-way blood flow.

In tissue-type valves, a whole xenograft valve (e.g., porcine) or aplurality of xenograft leaflets (e.g., bovine pericardium) typicallyprovide fluid occluding surfaces. Synthetic leaflets have been proposed,and thus the term “flexible leaflet valve” refers to both natural andartificial “tissue-type” valves. Two or more flexible leaflets aremounted within a peripheral support structure that usually includesposts or commissures extending in the outflow direction to mimic naturalfibrous commissures in the native annulus. Components of the valve areusually assembled with one or more biocompatible fabric (e.g., Dacron)coverings, and a fabric-covered sewing ring is provided on the inflowend of the peripheral support structure.

In most bioprosthetic-type valves, metallic or polymeric structureprovides base support for the flexible leaflets, which extend therefrom.One such support is an elastic “support frame,” sometimes called a“wireform” or “stent,” which has a plurality (typically three) of largeradius cusps supporting the cusp region of the flexible leaflets (i.e.,either a whole xenograft valve or three separate leaflets). The ends ofeach pair of adjacent cusps converge somewhat asymptotically to formupstanding commissures that terminate in tips, each extending in theopposite direction as the arcuate cusps and having a relatively smallerradius. The support frame typically describes a conical tube with thecommissure tips at the small diameter end. This provides an undulatingreference shape to which a fixed edge of each leaflet attaches (viacomponents such as fabric and sutures) much like the natural fibrousskeleton in the aortic annulus. One example of the construction of aflexible leaflet valve is seen in U.S. Pat. No. 5,928,281 to Huynh, etal. (Edwards Lifesciences, Corp., Irvine, Calif.), in which the explodedview of FIG. 1 illustrates a fabric-covered wireform 54 and afabric-covered support stent 56 on either side of a leaflet subassembly52.

Many other flexible leaflet valve configurations are known, includingU.S. Pat. No. 6,086,612 to Jansen (Adiam Medizintechnik GmbH & Co. KG,Germany) which discloses a mitral valve prosthesis having a supporthousing with a large base ring (12) that bears two stays (18, 19) whichsubstantially extend in the ring axis direction and are connected bycurved walls for securing two flexible cusps (leaflets). The free endsof the stays form an inner support for the cusps. The base-ring has inthe top view a closed, non-round shape with a common longitudinal axis(15) but two transverse half-axes (16, 17) of different sizes. The valveis symmetric about the combined transverse half-axes. The stays lie onthe longitudinal axis and form the transition between the two halves ofthe valve. The less curved wall (13) carries a mural cusp having asmaller surface and a higher angle of inclination relative to the basering base surface than the leaflet connected to the more curved wall(14). The material for the cusps (leaflets) can be synthetic resin foilsknown from the state of the art, preferably thermoplastic elastomers orsynthetic resins with elastomeric properties such as a flexiblepolyurethane foil.

Another flexible leaflet valve configuration is disclosed in U.S. Pat.No. 6,171,335 to Wheatley, et al. (Aortech Europe Limited, GreatBritain). This valve includes a generally annular frame with three postsand three scallops. The frame is tri-symmetric with an axis of symmetrydefined by the axis of blood flow through the valve. Each leaflet has atruncated spherical surface adjacent to its free edge that is joinedtangentially to a truncated conical surface. The leaflet surface isaxi-symmetrical with the axis of symmetry being perpendicular to theaxis of the valve frame and blood flow. The leaflets can comprise anybiostable, biocompatible thermoplastic elastomer including but notlimited to any polyurethane or silicone elastomer or any copolymer orblend based on these elements.

U.S. Pat. No. 6,613,086 to Moe, et al. (CarboMedics Inc., Austin, Tex.)discloses a tri-leaflet prosthetic cardiac valve with leaflets having ananalytic shape in a selected position. The leaflets are connected to avalve body at attachment curves. The shape of the leaflet is selectedfrom a set of geometries that can be represented mathematically. Theattachment curve is selected to improve the durability of thetri-leaflet valve by moving the point of maximum loaded stress along theattachment curve away from the commissures. An inner wall of the valvebody is given a non-circular shape near the attachment curve, the shapeof the inner wall corresponding to the attachment curve.

Unfortunately, some proposed valves deteriorate quickly, and someinordinately restrict flow which undesirably reduces the amount ofoxygen supplied to the body. The manufacturing process of tissue heartvalves is very mature and complex from the quality control point ofview, and only minimal improvements in valve durability have beenachieved in recent years. Accordingly, despite much development work onheart valves in the past three decades, there remains a need for a moredurable valve that permits more blood to flow.

SUMMARY OF THE INVENTION

The present invention provides a next-generation prosthetic heart valvehaving flexible leaflets that more closely approximates the actual shapeof a natural mitral valve. The prosthetic heart valve desirably includesan asymmetric base periphery and three flexible leaflets. Because of theasymmetry, one of the leaflets is larger than the other two.Simultaneously, the two commissure posts of the base that flank thelarger leaflet are taller than the other commissure posts. To helpincrease orifice valve area, the overall height profile of the valve hasbeen reduced so that the valve may be implanted intra-atrially. Certainaspects of the present invention may be applicable to prosthetic heartvalves indicated for implantation in other than the mitral position.

In accordance with one embodiment of the invention, a prosthetic heartvalve comprises a base structure having a non-circular central floworifice oriented around a flow axis, and three flexible leaflets mountedon the base structure and projecting into the flow orifice. Preferably,the non-circular central orifice is elliptical in shape. If the valve isindicated for placement in a mitral annulus, then the non-circularcentral orifice may be in the shape of a mitral annulus in its systolicphase (often a “D” shape).

The base structure may include a stent having three cusps on an inflowend and three commissures on an outflow end. The three flexible leafletseach include a cusp edge terminating in a pair of commissure edges, witha free edge extending between the commissure edges and opposite the cuspedge. Each leaflet attaches along its cusp and commissure edges to acusp and two associated commissures of the stent. In one embodiment, thestent includes a wireform having cusps and commissures, and each leafletcommissure edge includes a tab that extends radially outward withrespect to a wireform commissure and attaches on the outer side thereof.The stent may further include a primary band having an outflow edge thatmimics the alternating cusp and commissure shape of the wireform and islocated radially outward from the wireform. The leaflet tabs attach tothe band outward from the wireform commissures. In addition, a secondaryband surrounding the primary band may be provided to add rigidity to acommon inflow edge thereof.

Desirably, at least one of the three flexible leaflets is configureddifferently than one of the others. For example, one of the threeflexible leaflets may be substantially larger than the other two. If theprosthetic heart valve is oriented for placement within the mitralannulus, the larger leaflet is on an anterior side of the valve and thetwo smaller leaflets are on a posterior side of the valve. In apreferred embodiment, the base structure includes a stent having threecusps on an inflow end and three commissures on an outflow end. Thethree flexible leaflets each include a cusp edge terminating in a pairof commissure edges, with a free edge extending between the commissureedges and opposite the cusp edge. Each leaflet attaches along its cuspand commissure edges to a cusp and two associated commissures of thestent, and the two commissures of the stent to which the larger leafletattaches may have greater dimensions along the flow axis than the thirdcommissure.

In accordance with another aspect of the invention, a prosthetic heartvalve is provided that has a base structure having a central floworifice oriented around a flow axis. Three flexible leaflets mount onthe base structure and project into the flow orifice, and at least oneof the three flexible leaflets is configured substantially differentlythan at least one of the others. For example, one of the three flexibleleaflets is substantially thicker than the other two. Alternatively, orin addition, one of the three flexible leaflets is substantially largerin occluding area than the other two.

If the prosthetic heart valve is oriented for placement within themitral annulus, the larger leaflet is on an anterior side and the twosmaller leaflets are on a posterior side. If the prosthetic heart valvehas the aforementioned base structure with a stent having commissures,then the two commissures of the stent to which the larger leafletattaches have greater dimensions along the flow axis than the thirdcommissure. The central orifice of the valve may be elliptical anddefine a major axis and a minor axis. Preferably, the minor axis bisectsthe larger leaflet. In one embodiment, the central orifice is in theshape of a mitral annulus in its systolic phase, with a longer dimensionand a shorter dimension in plan view. In the latter embodiment, an axisextending generally along the shorter dimension of the central orificebisects the larger leaflet.

In accordance with a still further aspect of the invention, a prostheticheart valve has a plurality of flexible leaflets and a base structure onwhich the leaflets mount. The base structure has a central flow orificeoriented about a flow axis and includes a stent having a plurality ofcusps on an inflow end and the same number of commissures on an outflowend. At least one of the commissures has a different axial dimensionthan at least one other commissure. The central orifice may benon-circular, for example elliptical. Or, the prosthetic heart valve maybe configured for placement in a mitral annulus, wherein thenon-circular central orifice is in the shape of a mitral annulus in itssystolic phase.

The flexible leaflets each may include a cusp edge terminating in a pairof commissure edges, with a free edge extending between the commissureedges and opposite the cusp edge. The stent desirably includes a wireform having cusps and commissures, wherein each leaflet attaches alongits cusp and commissure edges to a cusp and two associated commissuresof the stent. Preferably, at least one of the flexible leaflets isconfigured differently than one of the others. For example, one of theleaflets may be larger in occluding area than the other leaflets. Inthis embodiment, at least two of the commissures of the stent havegreater dimensions along the flow axis than at least one othercommissure, wherein the larger flexible leaflet attaches to the twolarger stent commissures. If the prosthetic heart valve is oriented forplacement within the mitral annulus and has three flexible leaflets, thelarger leaflet is positioned on an anterior side and two smallerleaflets are positioned on a posterior side. Preferably, at least one ofthe commissures has an axial dimension that is less than about 85% ofthe axial dimension of at least one of the other commissure.

The invention also contemplates a prosthetic heart valve having a loweroutflow profile, comprising a base structure and a plurality of flexibleleaflets mounted thereon. The base structure has a central flow orificeoriented around a flow axis, and the mounted leaflets project into theflow orifice. The leaflets are mounted in the base structure so as todefine a leaflet axial dimension from their inflow ends to their outflowends thereof. The valve also includes a sewing ring mounted around thebase structure at an attachment elevation. To provide the low profile,the distance between the attachment elevation and the outflow end of theleaflets relative to the leaflet axial dimension is less than about 75%.

The present invention also provides a prosthetic mitral heart valvesuitable for intra-atrial implant. The intra-atrial valve includes abase structure having a central flow orifice oriented around a flowaxis, the base structure including a stent having a plurality of cuspson an inflow end and the same number of commissures on an outflow end. Aplurality of flexible leaflets mount on the base structure and projectinto the flow orifice. A sewing ring mounts around the base structuresuch that none of the commissures of the base structure projects axiallyin the outflow direction from the attachment line of the sewing ring farenough to contact and injure the interior of the left ventricle.Preferably, the sewing ring has a scalloped inflow profile.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1 and 2 are perspective and elevational views, respectively, of ananatomically approximate prosthetic mitral heart valve of the presentinvention;

FIGS. 3 and 4 heart topic and bottom plane views, respectively, of theprosthetic mitral heart valve of FIG. 2;

FIGS. 5A-5C are perspective, plan, and elevational views, respectively,of a wireform or stent forming a part of a base structure of anexemplary prosthetic mitral heart valve of the present invention;

FIGS. 6A and 6B are perspective exploded and assembled views of asupport band combination forming a part of the base structure of anexemplary prosthetic mitral heart valve of the present invention;

FIGS. 7A-7C are cross-sectional views of the assembled support bandcombination taken along the indicated section lines in FIG. 6B;

FIGS. 8A and 8B are perspective and top plan views, respectively, of anexemplary sewing ring sponge used in conjunction with the exemplaryvalve base structure to create a low-profile heart valve and thereforeenable intra-atrial placement in the mitral position;

FIGS. 9A-9C are cross-sectional views of the assembled prosthetic mitralheart valve taken along the indicated section lines in FIG. 3; and

FIGS. 10A and 10B are plan views of two dissimilar flexible leafletsutilized in the prosthetic heart valve of the present invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

The present invention pertains to prosthetic heart valves that simulatethe natural human heart valve anatomy, in particular for the mitralvalve. For instance, the shape of the flow orifice is non-circular so asto mimic the shape of the mitral annulus in the systolic phase. Also, ina preferred embodiment three leaflets are utilized with at least onebeing substantially different than the other two. The reader will seefrom the following description and appended drawings various features ofthe exemplary valves that are intended to mimic the natural mitralvalve. However, because of the nature of prosthetic heart valves interms of durability and implantation requirements, a prosthetic valvecannot precisely mirror a natural valve. Accordingly, the prostheticmitral valve disclosed herein is termed “anatomically approximate” toindicate one or more modifications from conventional prosthetic valvesthat render it more like a natural valve. It should be noted that one ormore of these features that render the valve “anatomically approximate”may be applicable to prosthetic valves for implantation in other thanthe mitral position, such as in the aortic position. As such, unless afeature is specifically applicable to the mitral position the inventionshould not be considered so limited.

Several considerations drive the development of an anatomicallyapproximate heart valve. For instance, in the mitral position the nativeanatomy comprises a relatively large anterior leaflet extending betweenthe fibrous trigones and a posterior leaflet commonly subdivided intothree scalloped shapes. In the systolic phase, the mitral annulusgenerally assumes an oval or elliptical shape with a short or minor axisapproximately bisecting the anterior leaflet, midway between thetrigones. Conventional prosthetic heart valves have circular basestructures creating a circular orifice, which may not be an optimumshape to facilitate active opening of the leaflets and maximum flowthrough the orifice. The present invention provides a valve with a basestructure that mimics the shape of the mitral annulus in the systolicphase and facilitates active opening of the leaflets and better bloodflow. In addition, the more naturally-shaped base structure inconjunction with leaflets that better simulate the native leaflets isbelieved to reduce stresses imposed on various components of theprosthetic valve because the structure more faithfully simulates thenative anatomy. Less stress on the valve may lead to a more durableimplant. These and other design considerations were factors in thedevelopment of the present invention.

One of the features that makes the present prosthetic heart valve moreanatomically approximate is that one flexible leaflet is larger than theother two. Because there are three leaflets, the larger leaflet spans acircumferential angle of more than 120°. Accordingly, the adjacentcommissure posts of the base structure are somewhat larger thanprosthetic valves of the prior art. In the mitral position, the outflowend of the valve projects toward and into the left ventricle. Tocompensate for the larger commissure posts which might extend far enoughto contact and injure the interior of the left ventricle, the presentinvention provides an innovative sewing ring in conjunction with thevalve base structure such that the valve can be positioned farther intothe left atrium. This implant position is termed “intra-atrialplacement” because the valve is sewn to the atrial side of the mitralannulus, as opposed to within the annulus (intra-annular). Because ofthe mitral anatomy at this location, the sewing ring has a scallopedinflow profile which is different than previous annular mitral valvesewing rings. Though it is well-known to provide a scalloped orundulating sewing ring for prosthetic aortic valves, the presentapplication is believed to be the first to incorporate such structureinto a mitral valve sewing ring.

For definitional purposes, heart valves of the present invention are ofthe flexible leaflet type, as opposed to mechanical valves with rigidleaflets or balls for occluding members. The term “flexible leaflet”encompasses bioprosthetic leaflets such as bovine pericardium, leafletsin whole xenograft (e.g., porcine) valves, bioengineered materials, andsynthetic leaflets. The flexible leaflets are mounted from a peripheralbase structure so as to project inward into a flow orifice defined bythe base structure.

The term “base structure” broadly covers structures having wireform,stents, and the like. For example, the exemplary embodiment of thepresent invention includes an undulating cloth-covered wireform to whichperipheral edges of three leaflets are sewn. The term “cloth” as usedherein encompasses a variety of biocompatible fabrics, the most commonlyused being polyester terephthalate. Additionally, a dual-band structuresurrounds the wireform and provides additional support for the leaflets.Another similar base structure is disclosed in U.S. Pat. No. 6,350,282to Medtronic, Inc. of Minneapolis, Minn. Another base structuredisclosed in U.S. Pat. No. 5,824,069 to Medtronic, Inc. has a “stent” asa base structure that supports flexible leaflets. The stent defines anundulating outflow edge, similar to a wireform. It should also be notedthat a “wireform” could be made from a variety of materials, includingbiocompatible metals such as Elgiloy and polymers such as Delrin.Another “base structure” that can be modified to incorporate certainfeatures of the present invention is shown in U.S. Pat. No. 6,610,088 toGabbay and includes a “stent” with an undulating outflow edge thatprovides support for flexible leaflets.

Finally, the term “base structure” encompasses conventional heart valvestents/wireforms designed to be delivered during open heart surgery, andalso compressible/expandable base structures designed forminimally-invasive surgeries, such as shown in U.S. Pat. No. 5,411,552to Andersen, et al. The patent to Anderson, et al. also discloses awhole cardiac valve connected to the stent structure which is avariation covered by the term “flexible leaflets.”

With reference now to FIGS. 1-4, an exemplary prosthetic heart valve 20of the present invention is shown in various views. In general, theheart valve 20 includes a plurality of flexible leaflets 22 a, 22 b, 22c supported by a peripheral base structure 24 and projecting inwardlytherefrom toward a central flow axis 26. A suture or sewing ring 28attaches around the outside of the base structure 24 and provides aplatform through which attachment structure may be passed to hold thevalve 20 in place within the body. Typically, heart valves are securedwithin the affected annulus using an array of sutures passed through thesewing ring 28, although staples, clips, and other such devices mayalternatively be used.

The heart valve 20 includes a plurality of commissures 30 a, 30 b, 30 c,the latter being smaller in axial dimension, as seen in elevation inFIG. 2. The upper tips of the commissures 30 a, 30 b, 30 c define anoutflow end of the valve 20 while the lower extremity of the sewing ring28 defines an inflow end. As will be clear below, each of the leaflets22 a, 22 b, 22 c includes a peripheral cusp edge that attaches aroundthe base structure 24 between two adjacent commissures 30, a pair ofcommissure edges on either end of the cusp edge that attach to the twocommissures, and a free edge 32 a, 32 b, 32 c (see FIG. 3) that extendsacross the flow orifice between the two commissures. As with manyconventional flexible leaflets valves, the leaflets 22 a, 22 b, 22 cproject into the flow orifice toward the axis 26 and meet or “coapt” ina tri-foil configuration. The valve 20 is shown in the figures in itsclosed state with the leaflets 22 a, 22 b, 22 c coapting together alongthree lines radiating generally from the flow axis 26.

With reference to FIG. 2, the heart valve 20 has an axial height asindicated at Z₁ from the inflow end to the outflow end. As illustrated,the axial height Z₁ extends from the lowermost point of the sewing ring28 to the tip of one of the two larger commissures 30 a or 30 b. In theexemplary heart valve 20, this axial height Z₁ is approximately equal tothe axial dimension of the leaflets 22, at least at the two largercommissures 30 a, 30 b. As will be explained in more detail below, thecusp edge of each of the leaflets mounts to the base structure 24 alonga line that is close to the lowermost extent of the sewing ring 28, andextends upward into proximity with the tips of the commissures.Therefore, for purpose of definition in this valve embodiment, the valveaxial height Z₁ will be deemed analogous to the leaflet axial dimension.

The axial dimension Z₂ shown in FIG. 2 indicates the distance betweenthe uppermost surface 34 of the sewing ring 28 to the tip of one of thetwo larger commissures 30 a or 30 b. The uppermost surface 34 of thesewing ring 28 can be defined as an attachment elevation for the heartvalve 20. That is, the surgeon passes sutures or other devices throughboth the side surface 36 and the upper surface 34 of the sewing ring 28,essentially forming a loop around the outer periphery or apex 38, asindicated by the dashed line 40. Although there is no single plane ofattachment of the sewing ring 28, the upper surface 34 will be termedthe attachment elevation for purpose of reference.

The heart valve 20 of the present invention has a relatively low-profilefrom the sewing ring 28 to the outflow end. More precisely, thedimension Z₂ is smaller in proportion to the leaflet axial dimension Z₁,in comparison with heart valves of the prior art. An alternative way tosee this is that the taller commissures 30 a, 30 b project in theoutflow direction a shorter distance from the sewing ring 28 relative tothe valve axial height Z₁ in comparison to other prosthetic heartvalves, in particular prosthetic mitral valves. Preferably, the distancebetween the attachment elevation (sewing ring upper surface 34) and theoutflow end of the leaflets, relative to the leaflet axial dimension, isless than about 75%. For the mitral position, this construction enablesthe heart valve 20 to be implanted in the intra-atrial position. Thatis, the sewing ring 28 attaches to the tissue of the left atriumadjacent to the mitral annulus, rather than directly within the annulus.This low-profile commissure construction helps insure that the tallcommissures 30 a, 30 b do not undesirably project too far into the leftventricle, possibly causing injurious contact with the inner ventriclewall.

The reason that the commissures 30 a, 30 b are taller than those ofconventional heart valves of the same type is that one of the leaflets22 is configured substantially differently than at least one of theothers. Namely, one leaflet 22 a is substantially larger in occludingarea than the other two leaflets 22 b or 22 c. This can best be seen inFIGS. 3 and 4, which are plan views from the outflow and inflow ends,respectively.

The base structure 24 defines a non-circular flow orifice within whichthe three leaflets are supported. In the orientation of FIG. 3, thehorizontal dimension of the base structure 24 is greater than thevertical dimension, creating somewhat of an elliptical or oval shape.When utilized in the mitral position, the peripheral shape of the basestructure 24 is desirably in the shape of the mitral annulus in itssystolic phase, which is substantially elliptical or D-shaped. As anapproximate rule of thumb, the ratio of the minor axis (vertical)dimension to the major axis (horizontal) dimension is approximately 3:4,although it is believed that a ratio of 5:4 may be more suitable for theexemplary prosthetic mitral valve 20.

Still with reference to FIG. 3, when the heart valve 20 is to be used inthe mitral position, the leaflets 22 a, 22 b, 22 c are oriented toapproximately mirror the native leaflet orientation and relative sizes.That is, that the first leaflet 22 a extends between first and secondcommissures 30 a, 30 b that are spaced apart around the circumference ofthe valve 20 at the approximate location of the fibrous trigones of themitral annulus. Therefore, the first leaflet 22 a simulates the anteriorleaflet of the mitral annulus, and the upper portion 48 of the valve 20as shown in FIG. 3 represents an anterior aspect thereof. Conversely,the lower portion (not numbered) of the valve 20 as shown in FIG. 3,between the first and second commissures 30 a, 30 b, represents aposterior aspect. Of course, the valve 20 must be implanted in thisorientation to obtain the intended benefits.

As indicated in FIG. 4, the angular distance A around the anterioraspect of the base structure 24 between the first and second commissures30 a, 30 b is substantially greater than the angular distance P₁ fromthe first commissure 30 a to the third commissure 30 c, or the angulardistance P₂ from the second commissure 30 b to the third commissure 30c. The sum of the angular distances P₁ and P₂ represents the posterioraspect of the valve 20. In a preferred embodiment, the angular distanceA is between about 34-40%, and more preferably approximately 35% (125°),of the total angular distance around the valve periphery.

Because the first and second commissures 30 a, 30 b are spaced fartherapart than any other pair of commissures, the first leaflet 22 a issubstantially larger than the second and third leaflets 22 b, 22 c.Indeed, because the angular span of the first leaflet 22 a is greaterthan 120°, the heights of the first and second commissures 30 a, 30 bmust be taller than the third commissure 30 c (and taller thancommissures of prior art valves) to ensure that the three leaflets meetat the same elevation in the middle of the flow orifice. Also, it shouldbe noted that the first leaflet 22 a is desirably symmetric about aplane bisecting the leaflet between the first and second commissures 30a, 30 b, but the second and third leaflets 22 b, 22 c may not belikewise symmetric because they attach to commissures of unequalheights. The specific shape of the three leaflets will be describedbelow with reference to FIGS. 10A and 10B.

In one exemplary embodiment of the invention, existing prosthetic heartvalve leaflets may be used to construct the anatomically approximateheart valve 20. In general terms, heart valves are labeled by thediameter of their orifice, typically between 25 millimeters and 33 mm inodd increments (i.e., 25-27-29-31-33), which provides an adequateselection of sizes for most patients. For definitional purposes, a 29 mmheart valve 20 of the present invention has a nominal major axisdimension of 29 mm. The exemplary heart valve 20 may have a largerleaflet 22 a that is otherwise conventional but sized for use in alarger heart valve of the prior art (i.e., circular), while the smallerleaflets 22 b, 22 c may be indicated for use in a smaller heart valve ofthe prior art. For example, a 29 mm heart valve 20 of the presentinvention may utilize a single larger leaflet 22 a that would otherwisebe suitable for use in a conventional 33 mm prosthetic valve, while thetwo smaller leaflets 22 a, 22 b are sized for use in a conventional 27mm prosthetic valve. Another way to state this is that the larger(anterior) leaflet 22 a is preferably two sizes above the nominal sizeof the valve (e.g., 33 mm leaflet for a 29 mm valve), while the smaller(posterior) leaflets 22 a, 22 b are one size below (e.g., 27 mm leafletsfor a 29 mm valve).

FIG. 4 also illustrates an offset between the approximate flow axis 26(approximate because the leaflets are flexible and the precise center ofthe flow axis may vary) and the geometric center 42 of the valve 20. Thegeometric center 42 lies at the intersection of a major axis 44 and aminor axis 46 of the generally elliptical valve 20. The offset stemsfrom the uneven nature of the three coapting leaflets 22 a, 22 b, 22 c.

With reference again to FIG. 3, a preferred difference in the thicknessof the leaflets is shown. The free edge 32 a of the first leaflet 22 ais illustrated slightly thicker than the free edges 32 b, 32 c of thesecond and third leaflets 22 b, 22 c. Because of the larger area of thefirst leaflet 22 a, it will be subjected to a greater overall force fromthe pressure of the blood flow when the valve closes (the systolic phaseof the mitral valve). Therefore, at least for bioprosthetic tissue suchas bovine pericardium, it is desirable that the larger leaflet 22 a bemade somewhat more robust than the other two leaflets to have acomparable usable life (i.e., durability). In one embodiment, thethickness of the larger leaflet 22 a is between about 10-100% greaterthan the thickness of the other two leaflets.

In accordance with an exemplary fabrication method, the leafletselection methodology disclosed in U.S. Pat. No. 6,245,105 (expresslyincorporated herein) may be used to provide stronger tissue for thelarger leaflet 22 a than for the other leaflets. The selectionmethodology utilizes one or more tests, for example a deflection test,to determine the relative elasticity or stiffness of each leaflet.Because of the non-uniform nature of certain bioprosthetic tissue, forexample bovine pericardium, the same size leaflets cut from differentportions of tissue may have different mechanical properties. Inaccordance with an exemplary fabrication method, relatively stronger(e.g., stiffer) leaflets are selected for use as the larger leaflet 22a, but relatively softer membrane-like leaflets are used as the smallerleaflets 22 b, 22 c. It should be noted that these characteristics cangenerally be predicted merely from measuring the thickness of thetissue, but the supplemental selection methodology disclosed in U.S.Pat. No. 6,245,105 is desirably used to further distinguish betweenleaflets of the same thickness.

Wireform or Stent

FIGS. 5A-5C illustrate an exemplary wireform 50 that forms a part of thevalve base structure 24. In a preferred embodiment, the wireform 50comprises a wire-like metal alloy such as Elgiloy that may be formed anumber of ways. A conventional forming method is to bend a straight wireinto the three-dimensional shape and join the two free ends with a crimp52 as seen in FIG. 5A. Alternatively, a specially-shaped blank may beseparated from a sheet or tube of material and then bent into shapeusing heat treating, for example. In the latter method, the wireform 50starts out as a continuous closed blank, and therefore there is no needfor the crimp 52, as in FIGS. 5B and 5C. Furthermore, if the wireform 50is made of a polymer it can be molded directly into the continuousclosed shape shown.

The wireform 50 comprises alternating commissures 54 a, 54 b, 54 c onthe outflow end and cusps 56 a, 56 b, 56 c on the inflow end. Thecommissures 54 (sometimes termed posts) comprise relatively narrowconverging straight portions, terminating in arcuate tips withrelatively small radii. The cusps 56, in contrast, are continuouslycurved and have relatively large radii. As seen in the plan view of FIG.5B (and by the dashed line 57 connecting the cusp 56 midpoints in FIG.5A) the peripheral shape of the wireform 50 is generally elliptical witha major axis 58 and a minor axis 60. The relative orientation of thethree commissures 54 is seen again in FIG. 5B, with the first and secondcommissures 54 a, 54 b being spaced apart an angular distance of greaterthan 120°. The commissures 54 desirably angle slightly radially inwardlyfrom the adjacent cusps 56 so that the wireform 50 defines anapproximately conical shape.

In the exemplary construction of heart valve 20, the peripheral edges ofthe leaflets attach to the wireform 50, and therefore the wireform(sometimes termed the “stent”) defines the shape of the flow orifice andthe three-dimensional support structure for the leaflets. The contour ofthe wireform 50 (or stent) thus defines the leaflet axial dimension. Itis worth repeating here that the heart valve 20 preferably has a sewingring attachment line that is closer to the outflow end of the valverelative to the leaflet axial dimension (stent height) as compared withvalves of the prior art. As stated above, other valve constructions maynot utilize a wireform, but the same principles apply with respect tothe low-profile sewing ring, albeit relative to wherever the leafletsattach.

The total axial height h₁ of the wireform 50 is indicated in FIG. 5C andextends from a plane in which lie the three cusps 56 a, 56 b, 56 c tothe tips of the equally sized first and second commissures 54 a, 54 b.The axial height h₂ of the third commissure 54 c is less than h₁,preferably less than about 85% of h₁. Because the three commissures 54perform essentially the same function, that of resiliently supportingthe commissure edges of two adjacent leaflets, they are similarly shapedif not equally sized.

The commissure heights of the exemplary wireform 50 may be compared withthe heights of the commissures of conventional valves to provide a levelof context. For an exemplary heart valve 20 of the present inventionlabeled for use in a 29 mm annulus, the axial height h₂ of the thirdcommissure 54 c is desirably about 3 mm less than the height of acommissure of a conventional 29 mm prosthetic heart valve. From the samevalve, the axial height h₁ of the first and second commissures 54 a, 54b is desirably about 1 mm less than the height of a commissure of aconventional 29 mm prosthetic heart valve. It should be noted that theserelative dimensions are derived by comparing an exemplary 29 mm mitralheart valve 20 of the present invention with a 29 mm prosthetic mitralheart valve sold under the trade name Carpentier-Edwards PERIMOUNTPericardial Bioprosthesis by Edwards Lifesciences of Irvine, Calif.

Support Bands

FIGS. 6A and 6B illustrate, respectively, exploded and assembled viewsof a support band combination 70 that forms a part of the valve basestructure 24. The support band combination includes a primary band 72and a secondary band 74 surrounding the primary band. The primary band72 defines a closed shape similar to the wireform 50 described above,and includes an outflow edge 76 with alternating commissure sections 78a, 78 b, 78 c and cusp sections 80 a, 80 b, 80 c. The secondary band 74also defines a closed shape similar to the primary band, and has anoutflow edge 82 with commissure sections 84 a, 84 b, 84 c and cuspssections 86 a, 86 b, 86 c. The outflow edge 76 of the primary band 72 isshaped to closely follow the contours of the wireform 50. As such, thefirst and second commissure sections 78 a, 78 b are taller than thethird commissure section 78 c. Although the commissure sections 84 ofthe secondary band outflow edge 82 are truncated with respect to thoseof the primary band 72, the first and second sections 84 a, 84 b aretaller than the third section 84 c. These different heights are seenbest in FIGS. 7A and 7B.

As seen by the assembled view of FIG. 6B, and the cross-sections ofFIGS. 7A-7C, the secondary band 74 closely surrounds and is coupled tothe primary band 72. Although not numbered, the inflow edges of the twobands 72, 74 coincide to form a single common inflow edge in theassembled combination. FIG. 6B illustrates in partial cut-away a clothcovering 90 encompassing the combination. The cloth covering 90 isrolled into a cuff 92 that extends outward from the two bands along thecusp sections 80, 86, and partially up the commissure sections 78, 84.The cuff 92 is seen in cross-section in FIG. 7C and provides a sewingrim facilitating assembly of the valve, as will be described below. Thetwo bands 72, 74 include a number of radial holes through which couplingsutures (not shown) can be passed for joining the two bands together,and for securing the cloth covering to the combination.

In a preferred embodiment, the primary band 72 is formed of a materialthat is relatively more flexible than the secondary band 74. As willbecome clearer below, the flexible leaflets of the valve attach to theuppermost portions of the commissures of the flexible primary band 72,which does not inhibit flexing of the valve commissures during thesystolic, or valve closing, phase. Conversely, the more rigid secondaryband 74 provides stability to the basic structure around the inflow edgeand cusps. For example, the primary band 72 may be formed of a polymersuch as Delrin while the secondary band 74 is form of a metallic alloysuch as Elgiloy.

Exemplary Low-Profile Sewing Ring

As mentioned previously, the preferred use for the anatomicallyapproximate prosthetic heart valve 20 is in the mitral annulus. Becauseof the large anterior leaflet and taller commissures, the valve 20desirably seats farther into the left atrium than prior art mitral heartvalves to help prevent contact of the commissures with the interior ofthe left ventricle. This implant position is termed intra-atrial becausethe sewing ring is positioned on the atrial side of the mitral annulus,rather than within the annulus. To accomplish this, the aforementionedsewing ring 28 is wider in the radial direction and attaches to the basestructure 24 relatively closer to the outflow end of the valve incomparison with conventional valves.

FIGS. 8A and 8B are two views of an exemplary sewing ring sponge 100that makes up the primary component of the sewing ring 28 shown inFIG. 1. That is, the sewing ring 28 comprises the sponge 100 with acloth covering 102, seen in FIGS. 9A-9C. It should be understood thatthough the sewing ring sponge 100 is desirably a molded silicone rubberelement, other materials and fabrication techniques may be used to forma suture-permeable, contoured sewing ring. For purpose of orientation,the outflow direction of the valve is up in FIG. 8A.

The sponge 100 comprises a plurality of walls of approximately equalthickness defining multiple opens cells therebetween. With reference toFIG. 8B, the sponge 100 includes an outer wall 104, an intermediate wall106 spaced inwardly from outer wall, and an inner wall 108 that definesthe innermost surface of the sponge. The elliptical outflow rim 110 ofthe outer wall 104 extends in a plane and defines the outermost extentof the sponge 100. The outer wall 104 includes a short axial segment onthe outflow end, but curves inward toward the inflow end and terminatesin a scalloped inflow edge 112. The inflow edge 112 defines anundulating shape that generally mirrors the up and down contours of thewireform 50 of the valve. The intermediate wall 106 is orientedsubstantially axially and in the elliptical shape of the outflow rim110. A plurality of generally radially oriented cell walls 114 extendsbetween and joins the outer wall 104 and intermediate wall 106, creatinga plurality of voids or cells 116.

The inner wall 108 has an undulating configuration as seen best in FIG.8A, with three elevated segments 120 a, 120 b, 120 c located at thecommissures of the valve and three gently downwardly curved segments 122a, 122 b, 122 c therebetween. A plurality of generally radially orientedcell walls 124 extends between and joins the intermediate wall 106 andinner wall 108 and defines a plurality of voids or cells 126. Justinward from the axial intermediate wall 106, the outflow edges of thedownwardly curved segments 122 define three arcuate ledges ordepressions on which are supported the three cusps of the base structure24.

With reference to FIG. 8B, the first and second elevated segments 120 a,120 b of the inner wall 108 correspond to the location of the first andsecond commissures 30 a, 30 b of the base structure 24, as seen inFIG. 1. The third elevated segment 120 c corresponds to the location ofthe third commissure 30 c. FIG. 8B illustrates the non-symmetricpositioning of the three elevated segments 120 a, 120 b, 120 ccorresponding to the same positions of the valve commissures. Likewise,the three downwardly curved segments 122 a, 122 b, 122 c correspond tothe location of the three wireform cusps 56 a, 56 b, 56 c, seen in FIG.5A. The curvature of the outflow edges of the segments 122 matches therespective curvatures of the wireform cusps 56 such that the basestructure 24 fits closely within the intermediate wall 106 of the sponge100 and a portion thereof is supported by the ledges created by theundulating inner wall 108. This beneficial construction is shown in FIG.9B, and described below.

It is the depth of the three downwardly curved segments 122 a, 122 b,122 c from the outflow rim 110 that provides the “low-profile”characteristic of present valve 20. That is, the cusps of the basestructure 24 seat within the sewing ring 28 farther from the outflow rim110 than in previous valves. Desirably, the axial depth of the midpointof the segments 122 from the outflow rim 110 is greater than about 80%of the overall axial dimension of the sponge 100. At the same time, thescalloped inflow edge 112 provides a contour that matches the typicalanatomical contour of the left atrium adjacent to the mitral annulus.Because the sewing ring 28 attaches farther into the left atrium, thiscontour reduces interference with the natural movement of the atrium.Stated another way, the contour of the inflow edge 112 is designed tofollow the undulating fibrous “skeleton” of the mitral annulus on theatrial side.

Valve Construction

Now with reference to FIGS. 9A-9C certain details with regard toassembly of the various aforementioned components will be explained.FIGS. 9A-9C are taken along the section lines indicated in FIG. 3 at thelocations of, respectively, the smaller valve commissure, a midpoint ofa valve cusp, and a larger valve commissure. The three cross-sectionsare shown across the page, with the two commissure views at theirrelative axial elevations because the outflow rim 110 of the sewing ringsponge 100 remains planar around the periphery of the valve.

FIG. 9A shows the smaller valve commissure with the section line passingthrough a solid radial wall portion of the sewing ring sponge 100. Thecloth covering 102 around the sponge 100 is seen here. The basestructure 24 sits within the sewing ring 28 at the commissures. Moreparticularly, the base structure at the small valve commissure 30 cincludes the smaller commissure sections of the primary band 72 andsecondary band 74 positioned slightly radially outwardly from thesmaller commissure 54 c of the wireform 50. The cloth-covered supportband combination 70 is sized to fit closely within the cloth-coveredinner wall 108 of the sewing ring 28.

As seen at the top of FIG. 9A, the wireform is enclosed within a clothcovering 130 having two free ends that are joined together to form acloth flange 132. Although not shown, the cloth covering 130 and flange132 extend the entire way around the wireform 50 and provide a platformthrough which sutures may be passed to connect the wireform to the othercomponents of the valve. More particularly, sutures connect the flange132 to the flexible leaflets 22 (one of which, 22 c, is visible) and tothe cloth-covered primary support band 72. It should be noted at thispoint that the various sutures used to assemble components of the valveare not shown in the drawings for clarity.

The flexible leaflets 22 (shown in plan view in FIGS. 10A and 10B) eachinclude a pair of tabs 140 on either side of the free edge 32.Desirably, the tabs extend outward between the converging segments ofthe wireform commissures 54 and wrap around the respective commissuresection 78 c of the primary band 72. The tabs are attached with sutureson the outside of the primary band 72 and a further cloth patch 142 maybe added to encompass the commissure structure. Connecting the leaflettabs 140 to the base structure 24 in this manner greatly reducesstresses imposed on the attachment sutures. Because systolic forces onthe leaflets are greatest at the commissure tips, it follows that forceson the attachment sutures may also be concentrated at this location. Byattaching the tabs 140 on the outside of the primary band 72, thestresses are diffused through the support band and also by the wireformcommissure 54. This construction is shown and described in U.S. Pat. No.5,928,281 to Huynh, et al., the disclosure of which is hereby expresslyincorporated by reference.

FIG. 9B is a section through a valve cusp, and illustrates the variouswalls of the sewing ring sponge 100. Namely, the outer wall 104 has anarcuate shape that extends substantially below its location at thecommissure (FIG. 9A), the vertical intermediate wall 106 is dimensionedto receive the valve base structure 24, and the inner wall 108 at itslowest point defines a ledge on which a portion of the base structureseats. The base structure 24 at the cusps include the cusp sections ofthe support band combination 70, a wireform cusp 56 c, and theassociated cloth coverings. Again, the cloth-covered support bandcombination 70 fits closely within the cloth-covered inner wall 108 ofthe sewing ring 28.

Particular attention is directed to the cloth flange 132 extendingoutwardly from the wireform which, along with the sewing rim or cuff 92of the support band combination 70 sandwiches a cusp edge 33 c of theleaflet 22 c. A line of attachment sutures (not shown) extends aroundthe valve cusps in this manner to provide a continuous, undulatingsupport of the leaflets by the base structure 24. Preferably, thewireform/leaflets/support band subassembly is formed prior to joiningwith the sewing ring 28. Again, the various attachment sutures are notshown for clarity.

Finally, FIG. 9C is a section through the taller valve commissure, andagain shows the sewing ring 28 having the same configuration as at thesmaller commissure in FIG. 9A. The taller commissure 30 b of the basestructure includes the taller commissure sections of the primary band 72and secondary band 74 positioned slightly radially outwardly from one ofthe taller commissures 54 b of the wireform 50. A portion of the largerleaflet 22 a is seen, which also attaches to the base structure in thesame manner as described above with respect to the smaller commissure.

Leaflet Configurations

FIG. 10A is a plan view of the larger leaflet 22 a showing theaforementioned free edge 32 a terminating on the both sides with tabs140. The arcuate lower cusp edge 33 a extends between the tabs 140opposite the free edge 32 a. Because the leaflet 22 a is supported atadjacent identical commissures, it is symmetric about a mid-planepassing through the flow axis 26. On the other hand, FIG. 10B shows oneof the smaller leaflets 22 b which may not be symmetric about the flowaxis 26. More area of the smaller leaflets 22 b may extend from the flowaxis 26 to the larger commissure than to the smaller commissure to whichit attaches. Of course, as indicated above, conventional leaflets havingdifferent sizes may be utilized which, in plan view, are generallysymmetric about a vertical plane through their cusps, but which foldinward within the valve so as to lie slightly asymmetrically because ofthe shape of the exemplary valve and location of the resulting flowaxis.

It will be appreciated that the invention has been described hereabovewith reference to certain examples or preferred embodiments as shown inthe drawings. Various additions, deletions, changes and alterations maybe made to the above-described embodiments and examples, and it isintended that all such additions, deletions, changes and alterations beincluded within the scope of the following claims.

1. A prosthetic heart valve comprising: a base structure having anelliptical central flow orifice oriented around a flow axis, wherein thebase structure includes a stent having three arcuate cusps on an inflowend and three upstanding commissures on an outflow end; a sewing ringhaving an outflow edge mounted around the stent such that thecommissures extend in the outflow direction from the sewing ring; andthree separate flexible leaflets each having a peripheral cusp edgemounted around a cusp of the stent so as to define a free edge extendinginto the flow orifice, wherein at least one of the three flexibleleaflets is substantially larger than the other two, and the prostheticheart valve is oriented for placement within the mitral annulus suchthat the larger leaflet is on an anterior side and the two smallerleaflets are on a posterior side, and further wherein the cusp edge ofeach flexible leaflet terminates in a pair of commissure edges, with thefree edge extending between the commissure edges and opposite the cuspedge, and wherein each leaflet attaches along its cusp and commissureedges to a cusp and two associated commissures of the stent, and whereinthe two commissures of the stent to which the larger leaflet attacheshave greater dimensions along the flow axis than the third commissure.2. The heart valve of claim 1, wherein the elliptical central orifice isin the shape of a mitral annulus in its systolic phase.
 3. The heartvalve of claim 1, wherein the stent includes a wireform having cusps andcommissures, and wherein each leaflet commissure edge includes a tabthat extends radially outward with respect to a wireform commissure andattaches on the outer side thereof.
 4. The heart valve of claim 3,wherein the stent further includes a primary band having an outflow edgethat mimics the alternating cusp and commissure shape of the wireformand is located radially outward from the wireform, wherein the leaflettabs attach to the band outward from the wireform commissures.
 5. Theheart valve of claim 4, further including a secondary band surroundingthe primary band and providing rigidity to an inflow edge thereof. 6.The heart valve of claim 1, wherein the flexible leaflets arebioprosthetic tissue leaflets and at least one of the three leaflets issubstantially thicker than the other two leaflets.
 7. The heart valve ofclaim 6, wherein the larger leaflet is the thicker leaflet.
 8. The heartvalve of claim 1, wherein an angular distance A around the basestructure between first and second commissures that support the largerleaflet is greater than an angular distance P1 from the first commissureto the third commissure, and greater than an angular distance P2 fromthe second commissure to the third commissure.
 9. The heart valve ofclaim 8, wherein the angular distance A is between about 34-40% of thetotal angular distance around the base structure.
 10. A prosthetic heartvalve, comprising: three separate flexible leaflets; a base structure onwhich the flexible leaflets mount having a central flow orifice orientedaround a flow axis and including a stent having three cusps on an inflowend alternating with three commissures on an outflow end, the flexibleleaflets each having a peripheral cusp edge mounted around a cusp of thestent so as to define a free edge extending into the flow orifice,wherein an angular distance A around the base structure between firstand second commissures is greater than an angular distance P₁ from thefirst commissure to a third commissure, and greater than an angulardistance P₂ from the second commissure to the third commissure, P₁ andP₂ being equal, and wherein the first and second commissures are ofequal axial dimension and the third commissure has an axial dimensionthat is less than about 85% of the equal axial dimensions of the firstand second commissures; and a sewing ring having an outflow edge mountedaround the stent such that the commissures extend in the outflowdirection from the sewing ring.
 11. The heart valve of claim 10, whereinthe central orifice is non-circular.
 12. The heart valve of claim 11,wherein the non-circular central orifice is elliptical.
 13. The heartvalve of claim 11, wherein the prosthetic heart valve is configured forplacement in a mitral annulus, and the non-circular central orifice issubstantially in the shape of a mitral annulus in its systolic phase.14. The heart valve of claim 10, wherein the cusp edge of each flexibleleaflet terminates in a pair of commissure edges, with the free edgeextending between the commissure edges and opposite the cusp edge, andwherein each leaflet attaches along its cusp and commissure edges to acusp and two associated commissures of the stent.
 15. The heart valve ofclaim 14, wherein the stent includes a wireform having cusps andcommissures, and wherein each leaflet commissure edge includes a tabthat extends radially outward with respect to a wireform commissure andattaches on the outer side thereof.
 16. The heart valve of claim 15,wherein the stent further includes a primary band having an outflow edgethat mimics the alternating cusp and commissure shape of the wireformand is located radially outward from the wireform, wherein the leaflettabs attach to the band outward from the wireform commissures.
 17. Theheart valve of claim 16, further including a secondary band surroundingthe primary band and providing rigidity to an inflow edge thereof. 18.The heart valve of claim 10, wherein at least one of the flexibleleaflets is configured differently than one of the others.
 19. The heartvalve of claim 18, wherein the flexible leaflet that is configureddifferently is substantially larger in occluding area than the otherflexible leaflets.
 20. The heart valve of claim 19, wherein theprosthetic heart valve is oriented for placement within the mitralannulus, and wherein the larger flexible leaflet attaches between thefirst and second commissures that are spaced apart around thecircumference of the valve at the approximate location of fibroustrigones of the mitral annulus such that the larger flexible leafletsimulates the anterior leaflet of the mitral annulus.
 21. The heartvalve of claim 18, wherein the thickness of the flexible leaflet that isconfigured differently is between about 10-100% greater than thethickness of the other leaflets.